As is known in the art, the piezoelectric transformer uses a piezoelectric vibrator. The piezoelectric vibrator has at least one pair of drive electrodes formed on and/or in a piezoelectric-ceramic plate. When an AC voltage is applied to the pair of drive electrodes, the plate vibrates due to the piezoelectric effect with a resonant mode such as a single wavelength resonant mode. When the plate is vibrating, variation of voltage potential is generated at any position of the plate. The variable voltage potential can be taken out from an output electrode formed on the position. A pair of output electrodes can be formed at different positions on the plate. Thus, the AC voltage applied to the drive electrodes as primary electrodes is transformed and is obtained at the output electrodes as secondary electrodes.
Since it is important for the piezoelectric transformer that the piezoelectric plate vibrates, it is a serious problem to support the transformer without suppression of the vibration. A waveform of the vibration has vibration nodes and antinodes. Therefore, the transformer is supported at positions corresponding to the vibration nodes.
On the other hand, leads are required to apply the input voltage to the primary electrodes and take out the transformed voltage from the secondary electrodes. Usually, lead wires are connected to the primary electrodes and the secondary electrodes. However, the lead connection points are not always at positions corresponding to the vibration nodes. The lead wires should be free without tension so as to interfere the vibration of the piezoelectric plate. The lead wires are troublesome for assembling, maintenance and other deal of an electrical circuit device, especially, a small-sized device.
Further, the primary and secondary electrodes are formed on different surfaces of the piezoelectric plate. Therefore, mounting and wiring operation of the transformer on a circuit board is complex. This results in large space for mounting the transformer on the circuit board and also in a high cost and large size of the circuit device.
Therefore, it is an object of the present invention to provide the piezoelectric transformer which has a simple structure of connection with an external circuit and is small sized.